System and method for circuit overcurrent protection

Abstract

In one aspect, the invention provides a system for protecting a plurality of circuits including a plurality of circuit protective devices wherein each circuit protective device includes a respective nominal current rating. According to one embodiment, the system includes current sensing circuitry configured to measure a current of each circuit protective device; and a controller configured to receive each of the measured currents. According to one embodiment, the controller is further configured to determine a ratio between a total current being carried by all of the circuit protective devices combined and a total nominal current rating of all of the circuit protective devices combined and employ the ratio to determine a modified nominal current rating of each circuit protective device, respectively. In a further embodiment, the controller is configured to generate an output signal to isolate a selected circuit selected from among the plurality of circuits based on the modified nominal current rating of the circuit protective device included in the selected circuit.

Description

BACKGROUND OF INVENTION[0001]1. Field of the Invention[0002]Embodiments of the invention relate generally to circuit overcurrent protection. More specifically, at least one embodiment relates to a system and method for isolating circuit protective devices.[0003]2. Discussion of Related Art[0004]In general, overcurrent protection for electrical circuits is provided by circuit breakers, fuses, or a combination of the two. These protective devices are selected and applied according to their current ratings to protect electrical circuits including electrical wires and cables as well as electrical appliances, motors, transformers and other electrical loads. Often an electrical system includes a main circuit breaker or main fuse that supplies a plurality of branch circuits that may each include a separate protective device.[0005]As used herein, the term “circuit protective device” refers to a device that provides overcurrent protection including overcurrent sensing and circuit isolation i...

AI Technical Summary

Benefits of technology

This approach reduces nuisance tripping, improves current measurement accuracy, and prevents unwanted isolation of critical loads by intelligently managing thermal loading and current ratings across multiple circuits.

Problems solved by technology

Overcurrent conditions can result from overloads and short circuits.

However, the fast action of a fuse in an overcurrent condition can sometimes result in nuisance failures in which a fuse opens on a temporary overload and must be then replaced.

Also, many circuit breakers require manual resetting after they open as a result of an overload.

Accordingly, existing approaches to circuit protection generally do not take into consideration how the thermal characteristics of the fuse may result in nuisance tripping because the design of the circuit protection is focused on the protection of the equipment and wiring that is supplied by the circuitry.

Another problem with existing approaches involves the use of current sensing circuitry (e.g., a current sensor) having an analog output that is supplied to an input of an analog-to-digital converter (“ADC”).

In particular, the accuracy and range of the ADC is limited by the size of the ADC (i.e., the number of bits included in the converter) and the selected resolution of the ADC.

These limitations reduce the accuracy of current sensing during some overcurrent conditions.

The above limitations on ADCs employed with current sensing circuitry may result in inaccuracies in current measurements, and accordingly, in inaccuracies in the overcurrent protection employed with the ADCs.

Yet another problem with existing approaches to overcurrent protection schemes is the fact that consideration of thermal loading is often addressed on a circuit-by-circuit basis.

That is, where a system includes a plurality of branch circuits, the thermal loading may be evaluated on a branch circuit-by-branch circuit basis and the thermal capabilities of the entire system may not be adequately addressed.

Thus the transfer switch may not include a main circuit protective device and the 100-amp rated transfer switch may be overloaded without any operation of a circuit protective device.

Such an approach may result in the unwanted isolation of critical loads.

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